No Phoenix! Like jcboy said, press and hold these three keys together: Shift, Command, and 3. If you see a thumbnail in the corner of your screen, click it to edit the screenshot.
For only a portion of the screen: Press and hold these three keys together: Shift, Command, and 4. Drag the crosshair to select the area of the screen to capture. To move the selection, press and hold Space bar while dragging.
The images will get automatically to your desktop.